Bis-1(1,2,4-triazole-3-selenols)

ABSTRACT

Novel bis-(1,2,4-triazole-3-selenols) of the formula

Brown et al.

[ Oct. 22, 1974 BlS-l(1,2,4-TRlAZOLE-3-SELENOLS) Inventors: John Colin Brown; Patrick Joseph Keogh, both of llford, England Assignee: llford Limited, llford, Essex,

England Filed: Dec. 17, 1971 Appl. No.: 209,339

Foreign Application Priority Data Dec. 22, 1970 Great Britain 60801/70 us. or. 260/308 R, 96/60 BF Int. Cl C07d 55/06 Field of Search 260/308 R References Cited UNITED STATES PATENTS 6/1972 Gunther 260/308 12/1972 Bailey 260/308 X Primary ExaminerJohn M. Ford Attorney, Agent, or FirmWender0th, Lind & Ponack [57] ABSTRACT Novel bis-( l,2,4-triazole-3-selenols) of the formula (la) A-X-A' wherein A and A each represents a 1,2,4-triazole radical bound in its 3-position to X, bound in its 5- position to an HSe-group, one nitrogen atom of each 1,2,4-triazole ring being bound to a hydrogen atom, an alkyl group, an aryl group or an aralkyl group, and X represents a direct link or, as a divalent linking group, an alkylene group having up to 10 carbon atoms or a linking group of the composition -(CH ),,,Y-(CH Y standing for an oxygen atom or a sulphur atom or a group -NR when R is a hydrogen atom or an alkyl group or an aryl group or animalkyl group and each of m and n are integers of O to 5, or X represents a phenylene nucleus or napthalene nucleus linking group.

12 Claims, No Drawings BIS-1 (l ,2,4-TRIAZOLE-3-SELENOLS) According to the present invention there is provided a bis(l,2,4-triazole-3-selenol) of the formula wherein A and A each represents a 1,2,4-triazole radical bound in its 3-position to X, bound in its S-position to an HSe-groups, one nitrogen atom of each 1,2,4- triazole ring being bound to a hydrogen atom, an alkyl group an aryl group or an aralkyl group, and X represents a direct link or, as a divalent linking group, an alkylene group having up to carbon atoms or a linking group of the composition -(CH ),,,Y-(CH Y standing for an oxygen atom or a sulphur atom or a group -NR where R is a hydrogen atom or an alkyl group or an aryl group or an aralkyl group and each of m and n are integers of 0 to 5, or X represents a phenylene nucleus or naphthalene nucleus linking group.

The bis-(l,2,4-triazole-3-selenols) of this invention may also be represented by the formula Alternatively these (l,2,4-triazole-3-selenols) may be represented by the formula wherein R,, R and X have the same meanings as in formula (lb) and the valence bonds not saturated by R R HSe and X indicate the double bonds in the 1,2,4- triazole rings. 5,5'-Bis-(l,2,4-triazole-3-selenols) corresponding to formulae la, [b and lc wherein each of R and R are selected from a hydrogen atom, alkyl prefer ably methyl and aryl preferably phenyl, aralkyl preferably benzyl and X is a direct link, an alkylene chain having 1 to 4, preferably 1 or 2 carbon atoms, a phenylene group or a linking group (CH ),,,Y(CH wherein Y is oxygen or sulphur, preferably a sulphur atom and each of m and n are integers of l to 5, preferably l or 2 are of particular interest.

The 5,5-Bis-(l,2,4-triazole-3-selenols) of the present invention may be of asymmetrical or preferably symmetrical structure, viz. R and R may be different from one another or preferably are identical.

If R, or R are not hydrogen atoms the bis-triazoles exist in different isomeric forms eg 7 Further it is to understood thatthe 5,5'-bis (l,2,4

triazole-3-selenols) of the present invention have been defined and formulated with reference to their selenol form but these compounds may exist and be produced in their tautomeric selenone form. For example the 5 ,5 '-bis-(1,2,4-triazole-3-selenol) of formula I may exist as an selenone of the general formula (V):

I; ll. (v)

According to another feature of the present invention symmetrical 5,5-bis-(l,2,4-triazole-3-selenols) as hereinbefore defined are prepared by reacting two mols of a selenosemicarbazide of the general formula where each of R R is a hydrogen atom or one of them is an alkyl, aryl or aralkyl group the remainder being hydrogen atoms with a mol of a dibasic acid chloride of the general formula Cl COXCO Cl where X is a divalent linking group as hereinbefore defined or a direct link in the presence of a base to form the acyl bis-selenosemicarbazide and then ring closing the acyl compound by heating it in a basic medium. Acyl bisselenosemicarbazides are described in our co-pending U.S. application Ser. No. 209,340. Preferably the acylation reaction is carried out in an organic solvent, e.g., methanol or pyridine at a reduced temperature. The ring closure reaction may be carried out in the presence of an alkali metal acetate, carbonate, hydroxide 'or ethoxide.

Preferably the above preparation is carried out intwo stages that is to say the acyl derivative is isolated and purified before it is ring closed.

Alternatively symmetrical 5,5'-bis(1,2,4-triazole-3- selenol)s as hereinbefore defined are prepared by heating together 2 mols of a selenosemicarbazide of the general formula (Vla) or (Vlb) and 1 mol of a diester of a dibasic acid of the general formula R OCO X COOR wherein each of R and R is an alkyl or aralkyl group and X has the meaning given above in an alkaline alcoholic medium and isolating and purifying the product.

Unsymmetrical 5,5'-bis( l,2,4-triazole-3-selenol)s as hereinbefore defined may be prepared by reacting a selenosemicarbazide of the general formula (Vla) or (Vlb) with an acid chloride-half ester of a dibasic acid of the general formula R OCO X C C1 wherein R and X have the meanings given above in the presence of a base to form the half-ester-acyl compound of the selenosemicarbazide used, isolating and purifying the compound obtained and then heating it with a mol of a selenosemicarbazide of the general formula (Vlb) or (Vla) respectively in an alkaline alcoholic medium and isolating the product.

Alternatively unsymmetrical 5,5 '-bis-( 1,2,4-triazole- 3-selenols) as hereinbefore defined may be prepared by reacting a mol of a selenosemicarbazide of the general formula (Vla) or (Vlb) with an excess of a diester of a dibasic acid of the general formula R OCOX- OCOR, wherein R R and X have the meanings given above in an alkaline alcoholic medium isolating and purifying the product obtained and then reacting the product with a mol of a selenosemicarbazide of the general formula (Vlb) or (Vla) respectively in an alkaline alcoholic medium and isolating and purifying the product.

The following dibasic acid chlorides are of use in the preparation of the symmetrical 5,5-bis-( 1,2,4-triazole- 3-selenols) in the first preparation hereinbefore set forth: g g

7 oo-o1 CHr-OOCI om-oo 01 rim-0001 CHZ C 0 C1 5,5'-bis-(l,2,4-triazole-3-selenols) in the second and fourth preparations hereinbefore set forth:

COOCH:

O OCH:

CH1CO OCHa T CI-Iz-C O OCH:

The fo llowing acid chloride-half esters 056165511:

acids are of use in the preparation of the unsymmetrical 5,5'-bis-( 1,2,4-triazole-3-selenols) in the third preparation as hereinbefore set forth:

1 cm-c 0 C1 (4) (VII) 4 phenylselenoseinicarbazide scribed by Jensen & Frederiksen. Z. anaorg. allgem. Chem. 230 31-3 (1936) Z-phenylselenosemicarbazide preparation described by Mautner & Kumler. J. Amer. Chem. Soc. 97-101 (1956) 4-ethylselenosemicarbazide preparation described by Huls & Renson Bull. soc. chim. Belges 65 684- (1966) 4-propylselenosemicarbazide preparation described by Colland-Charon, Huls & Renson, Bull. soc. chim. Belges 71 541-53 (1962) 1-phenylselenosemicarbazide and l-(p-tolyl) selenosemicarbazide preparation described by Colland-Charon, Huls & Renson, Bull. soc. chim. Belges 71 554-62 (1962) l-methylselenosemicarb azide, 2-methylselenosemicarbazide, 4-methy1selenosemicarbazide, preparations described by Jensen, Felbert, Pedersen & Svanholm Acta. chem. Scand. 20(1) 278-81 (1966) 4-(p-chlorophenyl) selenosemicarbazide and 4(p-methoxyphenyl) selenosemicarbazide preparations described by Bulka, Ahlens & Tucek Chem. Ber. (4) 1373-8 (1967) The 5,5'-bis-1,2,4-triazole-3-seleno1s of the present invention are of use as bleach-fix accelerators as described in our co-pending US. application Ser. No. 100,839, now US. Pat. No. 3,702,248.

Example 1 Preparation of 5,5'-bis( l,2,4-triazole-3-selenol).

(a) Oxalyl- 1 ,1 '-bis( selenosemicarbazide) Oxalyl chloride (3.0 g) was added with stirring to a slurry of selenosemicarbazide (6.4 g) in dry distilled pyridine (50 ml). After a vigorous reaction, the resulting dark red brown solution was stirred at room temperature for a further 3% hours. Water (50 ml) was m then added, and the mixture was evaporated in vacuo to give a black oily residue, which was dissolved in percent sodium hydroxide solution ml) and filtered. Acidification of the filtrate with glacial acetic acid (20 ml) gave oxalyl-l-l-bis (selenosemicarbazide) as an orange solid (1.2 g), m.p. 193 C (decomp.)

(b) 5,5-bis( l,2,4-triazole-3-selenol).

V Example 2 5,5-bis( l,2,4-triazole-3-selenol) (alternative preparation) Selenosemicarbazide (6.9 g) and diethyl oxalate (2.95 g) were added to a solution of sodium (1.15 g) in methanol (50 ml), and the mixture was heated under reflux for 16 hours. The solvent was then evaporated in vacuo, and water (50 ml) was added. The solution was filtered to remove any selenium and residual selenosemicarbazide. The filtrate was acidified with concentrated hydrochloric acid, giving an orange precipitate, which was filtered off, washed with hot ethanol and water, and dried. 5,5'-bis(1,2,4-triazole-3- selenol) obtained (3.5 g) had an infrared spectrum identical with that of the product prepared in Example 1.

Using the method described in Example 2, the compounds of the following Examples were prepared.

Example 3 Preparation of methylene-5,5 '-bis( l,2,4-triazole-3-selenol) Selenosemicarbazide (13.8 g) was reacted with diethyl malonate (8.0 g) in the presence of sodium methoxide to give 50 g of methylene-5,5'-bis( 1 ,2,4-triazole- 3-selenol) of m.p. 180 183 C (decomp).

Example 4 Preparation of ethylene-5,5 '-bis(1,2,4-triazole-3-selenol) Sclenoscmicnrbazide (13.8 g) was reacted with diethyl succinate (8.7 g) in the presence of sodium methoxide to give 5.4 g of ethylene-5,5-bis( 1,2,4-triazole-3- selenol) of m.p. 210 C (decomp).

Example 5 Preparation of methylene 5 ,5 -bis( 2-methyl- 1 ,2,4-triazole-3-selenol) 2-methylselenosemicarbazide (15.2 g) was reacted with diethyl malonate (8 g) in the presence of sodium methoxide for 22 hours to give 0.2 g of methylene 5,5 bis(2-methyl-1,2,4-triazole-3-selenol) of m.p. 189 C.

Example 6 Preparation of methylene-5,5-bis(4-methyl-1,2.,4-triazole-3-selenol) 4-methylenselenosemicarbazide 15.2 g) was reacted with diethyl malonate (8 g) in the presence of sodium methoxide for 22 hours to give 3.5 g of methylene-5,5- (4-methyl-1,2,4-triazole-3-selenol) of m.p. 204 C.

Example 7 Preparation of ethylene-5,5 '-bis(4-methyl-1,2,4-triazole-3-selen0l) 4-methylselenosemicarbazide (15.2 g) was reacted with diethyl succinate (8.0 g) in the presence of sodium methoxide for 18 hours to give 1.8 g ethylene-5,5- bis(4-methyll ,2,4-triazole-3-selenol) of mp. 244C.

Example 8 Preparation of ethylene-5,5'-bis(4-phenyl-1,2,4-triazole-3-selenol) 4-phenylselenosemicarbazide (10.7 g) was reacted with diethyl succinate (4 g) in the presence of sodium methoxide for 18 hours to give ethylene-5,5--bis(4- phenyl-l,2,4-triazole-3-selenol which sintered at 203 C.

Example 9 Preparation of 5,5 -bis(2-methyll ,2,4-triazole-3-selenol) Z-methylselenosemicarbahide (7.6 g) was reacted with diethyl oxalate (3. g) in the presence of sodium methyoxide for 2 hours to give 5,5'-bis(2-methyl-1,2,4 triazole-3-selenol) which sinteredl at 196 C.

Example 10 Preparation of 5,5 -bis( 4-methyll ,2,4-triazole-3-selenol) 4-methylselenosemicarbazide (7.6 g) was reacted with diethyl oxalate (3. g) in the presence of sodium methyoxide for half an hour to give 1.7 g of 5,5-bis(4- methyl-1,2,4-triazole-3-selenol which sintered at 231C.

Example 11 Preparation of (thiodiethylene)-5 ,5 -bis(4-methyl-1 ,2,4-triazole-3- selenol) 4-methylselenosemicarbazide (7.6 g) was reacted with the dimethyl ester of the B,8-thiodi-propionic acid (5 g) in the presence of sodium methoxide for 7 hours to give 1.2 g of (thiodiethylene)-5,5'-bis(4-methyll,2,4-triazole-3-selenol) of m.p. 200 C.

Example 12 Preparation of 5 ,5 '-bis(4-phenyl- 1 ,2,4-triazole-3-selenol) 4-phenylselenosemicarbazide (4 g) was reacted with In this film: the blue sensitive layer yellow colour coupler of the formula:

dtethyl oxalate (l.] g) in the presence of sodium methoxide for 6 hours to give 1.1 g of 5,5 -bis(4-phenyll,2,4-triazole-3-selenol) which sintered at 190 C. N CH3 Example 13 5 Preparation of g v v 7 n 7 WW I g i p-phenylene-5,5'-bis(4-methyl-l,2,4-triazole-3- the green sensitive layers each contained a magenta selenol) colour coupler of the formula:

soar 011200002115 NN C H /CH N\ C- as CI-IzOCOC2 0 (3H 4-methylselenosemicarbazide (7.6 g) was reacted the red sensitive layers each containe a cyan colour with dimethyl terephthalate (4.8 g) in the presence of coupler of the formula: sodium methoxide for 4 hours to give 3.7 g of p- "o s s phenylene-S,5'-bis(4-methyl-l,2,4-triazole-3-selenol) 37 of m.p. 307 c. N The compounds of the foregoing Examples correspond CONH to the formula N M "5 HSe seH 2 :5 Y i coin N 2 W W. R 3/ \1; R The following processing solutions were used in Ex- Wi ample l4. and are listed in the following table. a -d a- V FMHTIIABLEVW WW WWWM" COiOUl' Developer Sodium metaborate 80 g Example Y Sodium sulphite anhydrous 2.0 g Potassium bromide 1.0 g l, 2 Direct link Hydroxylamine sulphate 2.6 g 3 PCH 4-amino-N-ethyl-N-(B-hydroxy ethyl)- aniline sulphate g 5:333:33: -oH; 1 7 -CH2CH2 SIOD-FIX Sodium thiosulphate pentahydrate l7l g 8 CH2CH2- Sodium acetate anhydrous 31.4 g Sodium sulphite anhydrous 4.3 g Acetic acid glacial ml 0 Direct link CH3 2 196 Polassluyfl alum s 10 Direct link -CH3 4 1 231 Ammonium chloride 43 g 11 -CHzCH2SCH2-CH2 CH3 4 200 water 10 I litre I l Bleach-Fix 12 hnk 4 190 Disodium tetraborate decahydrate 12.5 g Boric acid 22.5 g Sodium hydroxide 10.0 g 13 -CH3 4 307 Ethylcnediamine tetraacetic acid l6.2 g

Disodium salt of ethylenediamine tetraacetic acid 3.5 g Ferric chloride (60 solution 95 g l Smtermg' Sodium sulphite anhydrous 4.0 g 7 Water to 1 litre In the Example which follows a colour negative film c ndi r Disodium salt of ethylenediainine was used which was made up as follows. emacelic acid 0.50 g Sodium carbonate anhydrous 4.5 g yq Q and Sllver C a \fvmghlzm Formaldehyde (40% "I.. solution) 10 ml Sensitivity mg Ag/dcclmctre Wetting Agent (8 '71 solution) l.7 ml

Water to 1 litre Non Stress Blue Sensitive l3.4 Colloidal Silver Filler Layer Green Sensitive 13.1 All processing solutions and wash water were used at Topcoat 750 F- lntralayer Sensitive 160 Pieces of a colour negative film as described e.g. in lsubcloat the U.S. Pat. application Ser. No. 100 839 were fogged nter ayer Red Sensitive 745 and processed in a processing sequence including the 'l'opcoat use of a bleach-fix bath. The metallic silver remaining g g se'tlsmve in the film at the end of the processing sequence was U C01! Base of ccnulosetriacmle measured by analysts and expressed in mg of Ag/- TOTAL 73.6 decimetre When the bleach-fix bath contained one of the specified bleach-fix accelerators a reduction in the amount of residual silver resulted.

The residual silver resulting when one of the accelerators which was one of the compounds of the present invention was used is expressed as a percentage of that obtained when no accelerator was used.

Example 14 Pieces of the colour negative film were processed as follows:

Colour developer 10 minutes Stop-fix 4 minutes Bleach-fix 6 minutes with and without accelerator Wash 4 minutes Conditioner 4 minutes Wash 4 minutes Dry The silver content of the pieces of film was analysed with the following results:

wherein each of R and R is selected from the group consisting of hydrogen, alkyl of l-3 carbon atoms, phenyl, tolyl, chlorophenyl, methoxyphenyl and benzyl and X is selected from the group consisting of a direct link, an alkylene chain having 1-10 carbon atoms, phenylene,naphthylene,-NH-- and a linking group(CH Y(CH wherein Y is an oxygen or sulphur atom and each of m and n is zero or an integer of from 1 to 5.

2. A 5,5-bis(l,2,4-triazole-3-selenol) according to claim 1, wherein each of R and R is selected from the group consisting of hydrogen, alkyl of 1-3 carbon atoms, phenyl and tolyl and X is selected from the group consisting of a direct link, an alkylene chain having l-4 carbon atoms, phenylene and a linking group -(CH ),,,-Y(CH wherein Y is an oxygen or sulphur atom and each of m and n is zero or an integer of from 1 to 5.

3. A 5,5'-bis-(l,2,4-triazole-3-selenol) according to claim 2, wherein each of R and R is selected from hydrogen, methyl and phenyl, and X is a direct link, an alkylene chain having 1 or 2 carbon atoms, a phenylene group or a linking group (CH ),,,--Y(CH wherein Y is sulphur and each of m and n is the integer l or 2.

4. A process for the preparation of a symmetrical 5,5- 'bis-( 1 ,2,4-triazole-3-selenol) defined in claim 1 which comprises reacting two mols of a selenosemicarbazide of the formula wherein each of R R is hydrogen or one of them is selected from the group consisting of alkyl of l-3 carbon atoms, phenyl, tolyl, chlorophenyl, methoxyphenyl and benzyl, the remainder of the R groups being hydrogen atoms, with 1 mole of a dibasic acid chloride of the formula ClCO -X COC1, where X is as defined in claim 1, in the presence of a base to form an acyl bisselenosemicarbazide and heating the acyl compound in a basic medium to effect ring closure of the acyl compound.

5. A process according to claim a wherein the acyl compound is isolated and purified prior to effecting ring closure thereof. y

6. A process according to claim. 4 wherein the acyla tion reaction is conducted in an organic solvent at a reduced temperature.

7. A process according to claim 6 wherein the ring closure reaction is conducted in the presence of an alkali metal acetate, carbonate, hydroxide or ethoxide.

8. A process according to claim 4 wherein the dibasic acid chloride is oxalyl-, malonyl-., succinyl-, adipinyl-, thiodiacetyl-, B,B'-thiodipropionyl-or terephthaloylchloride.

9. A process for the preparation of a symmetrical 5,5- -bis-( l,2,4-triazole-3-selenol) defined in claim 1 which comprises reacting two moles of a selenosemicarbazide of the formula wherein each of R R is hydrogen or one of them is selected from the group consisting of alkyl of l3 carbon atoms, phenyl, tolyl, chlorophenyl, methoxyphenyl and benzyl, the remainder of the R1 groups being hydrogen atoms, with one mole of a diester of a dibasic acid of the formula R OCOX-COOR wherein each of R and R is methyl or ethyl and X is as defined in claim 1, in an alkaline alcoholic medium and isolating and purifying the resultant product.

10. A process according to claim 9 wherein the diester of a dibasic acid is diethyloxalato, diethyloxalate, B,B-thiodipropionate or dimethyllterephthalate.

11. A process for the preparation of an unsymmetrical 5,5'-bis-(l,2,4-triazole-3-selenol) defined in claim 1 which comprises reacting one mole of a selenosemicarbazide of the formula in se Ri wherein Gasser R5 R 5 arryaegassrsaasman is selected from the group consisting of alkyl of 1-3 carbon atoms, phenyl, tolyl, chlorophenyl, methoxyphenyl and benzyl, the remainder of the R groups being hydrogen atoms, with an acid chloride-half ester of a dibasic acid of the formula R OCO X CO-Cl, where R,,, is methyl or ethyl and X is as defined in claim 1, in the presence of a base to form the half-ester-acyl compound of the selenosemicarbazide, isolating and purify- 12. A process for the preparation of an unsymmetrical 5,5'-bis-(l,2,4-tria2ole-3-selenol) defined in claim 1 which comprises reacting one mole of a selenosemicarbazide of the formula R S e Ru 12 wherein each of R R is hydrogen or one of them is selected from the group consisting of alkyl of 13 carbon atoms, phenyl, tolyl, chlorophenyl, methoxyphenyl and benzyl, the remainder of the R groups being hydrogen atoms, with an excess of a diester of a dibasic acid of the formula R OCOXCOOR where each of R and R is methyl or ethyl and X is as defined in claim 1, in an alkaline alcoholic medium, isolating and purifying the resultant product, reacting the purified product with one mole of a selenosemicarbazide of the formula (Vla) or Vlb) respectively in an alkaline alcoholic medium and isolating and purifying the product thus obtained. 

1. A 5,5''-BIS(1,2,4-TRIAZOLE-3-SELENOL) OF THE FORMULA
 2. A 5,5''-bis(1,2,4-triazole-3-selenol) according to claim 1, wherein each of R1 and R2 is selected from the group consisting of hydrogen, alkyl of 1-3 carbon atoms, phenyl and tolyl and X is selected from the group consisting of a direct link, an alkylene chain having 1-4 carbon atoms, phenylene and a linking group -(CH2)m-Y-(CH2)n-, wherein Y is an oxygen or sulphur atom and each of m and n is zero or an integer of from 1 to
 5. 3. A 5,5''-bis-(1,2,4-triazole-3-selenol) according to claim 2, wherein each of R1 and R2 is selected from hydrogen, methyl and phenyl, and X is a direct link, an alkylene chain having 1 or 2 carbon atoms, a phenylene group or a linking group -(CH2)m-Y-(CH2)n- wherein Y is sulphur and each of m and n is the integer 1 or
 2. 4. A process for the preparation of a symmetrical 5,5''-bis-(1,2, 4-triazole-3-selenol) defined in claim 1 which comprises reacting two mols of a selenosemicarbazide of the formula
 5. A process according to claim 4 wherein the acyl compound is isolated and purified prior to effecting ring closure thereof.
 6. A process according to claim 4 wherein the acylation reaction is conducted in an organic solvent at a reduced temperature.
 7. A process according to claim 6 wherein the ring closure reaction is conducted in the presence of an alkali metal acetate, carbonate, hydroxide or ethoxide.
 8. A process according to claim 4 wherein the dibasic acid chloride is oxalyl-, malonyl-, succinyl-, adipinyl-, thiodiacetyl-, Beta , Beta ''-thiodipropionyl-or terephthaloyl-chloride.
 9. A process for the preparation of a symmetrical 5,5''-bis-(1,2, 4-triazole-3-selenol) defined in claim 1 which comprises reacting two moles of a selenosemicarbazide of the formula
 10. A process according to claim 9 wherein the diester of a dibasic acid is diethyloxalato, diethyloxalate, Beta , Beta '' -thiodipropionate or dimethylterephthalate.
 11. A process for the preparation of an unsymmetrical 5,5''-bis-(1,2,4-triazole-3-selenol) defined in claim 1 which comprises reacting one mole of a selenosemicarbazide of the formula
 12. A process for the preparation of an unsymmetrical 5,5''-bis-(1,2,4-triazole-3-selenol) defined in claim 1 which comprises reacting one mole of a selenosemicarbazide of the formula 